The present invention relates to torsion spring suspensions for trailers, vehicles, and the like, and in particular to a torsion spring suspension having a replaceable torsion element cartridge.
Torsion spring suspensions offer an attractive alternative to leaf spring suspensions and solid axles since torsion spring suspensions typically offer improved handling, a smoother ride, and a lower center of gravity. However, torsion spring assemblies tend to be more costly due to the specialized parts and equipment required to manufacture them. Further, the specialized parts and equipment can lead to product inconsistency and warranty problems.
Some torsion spring assemblies utilize rubber as the torsional stress absorber However, rubber is sensitive to temperature changes, and hence, the torsion spring assembly load ratings and spring rates of such torsion spring assemblies may vary significantly with temperature. Further, such rubber suspension, can be difficult to assemble consistently since the rubber components must typically be frozen first to reduce their size by contraction. Still further, once the rubber is assembled into the torsion spring assembly, clips and brackets cannot be welded to the outer cartridge or axle tube of the assembly and the latter cannot be mounted by welding since high weld temperatures will damage the rubber. Also, such axle assemblies tend to be very heavy due to the extensive amount of high-durometer rubber they use.
Still other torsion spring assemblies utilize metal or other torsion bars instead of rubber. These assemblies typically require use of a motion limiter to control over-rotation or over-torquing of the torsion springs. However, present motion limiters transmit the overstress condition to the torsion spring axle tube in a way that causes the axle tube to prematurely fail. For example, the motion limiter is often a polygonally shaped plate that rotates in the axle tube, pressing outwardly on the flat sides of the axle tube during over-torquing of the torsion spring assembly and potentially causing the cross-sectional profile of the axle tube to plastically deform. When this happens, the limiter may well fail, and a completely new axle tube is required to repair the suspension. Further, with the axle tube damaged, internal parts cannot be readily removed and reused, hence requiring that substantially all of the major parts be discarded and a new torsion spring assembly be installed.
Thus, there is a need for a torsion spring assembly that requires less specialized parts and less specialized machinery to assemble, and which distributes stress in a manner reducing the tendency to plastically deform parts during overload and over-rotation conditions. Furthermore, there is a pronounced need for a torsion spring axle assembly having a safe and completely reliable motion limiter which will operate repeatedly without damaging the assembly or impairing its ability to function properly.